3.2 Arithmetic Operators

As unary operators they denote a positive or negative expression. As binary operators they add or subtract.

*, /

Multiplication and division are binary operators.

%

Modulo binary operator.

3.3 Logical and Comparison Operators

The table below outlines the logical and comparison operators available.

Table 3-2 Logical and Comparison Operators

Operator

Description

NOT

Returns true if the following condition is false, returns false if it is true.

OR

Returns true if either component condition is true, returns false if both are false

AND

Returns true if both component conditions are true, returns false if either is false

=, !=, <, >, <=, >=,<>

Comparison operators

3.4 Concatenation Operators

The table below outlines the concatenation operators available.

Table 3-3 Concatenation Operators

Operator

Description

||

Concatenates character strings

3.5 Binary Operators

The table below outlines the binary operators available.

Table 3-4 Binary Operators

Operator

Description

&

Bitwise AND if both operands are numbers; conditional AND if both operands are Boolean.

|

Bitwise OR if both operands are numbers; conditional OR if both operands are Boolean.

^

Bitwise exclusive OR (XOR)

3.6 Array Definition Operator

The { and } curly braces are array definition operators following the Java array initialization syntax. Arrays can be useful to pass to user-defined functions or to select array data in a SELECT clause.

Array definitions consist of zero or more expressions within curly braces. Any type of expression is allowed within array definitions including constants, arithmetic expressions or event properties. This is the syntax of an array definition:

{ [expression [,expression [,…]]] }

Consider the next statement that returns an event property named actions. The engine populates the actions property as an array of java.lang.String values with a length of 2 elements. The first element of the array contains the observation property value and the second element the command property value of RFIDEvent events.

SELECT {observation, command} AS actions
FROM RFIDEvent RETAIN ALL

The engine determines the array type based on the types returned by the expressions in the array definition. For example, if all expressions in the array definition return integer values then the type of the array is java.lang.Integer[]. If the types returned by all expressions are a compatible number types, such as integer and double values, the engine coerces the array element values and returns a suitable type, java.lang.Double[] in this example. The type of the array returned is Object[] if the types of expressions cannot be coerced or return object values. Null values can also be used in an array definition.

Arrays can come in handy for use as parameters to user-defined functions:

SELECT *
FROM RFIDEvent RETAIN ALL
WHERE Filter.myFilter(zone, {1,2,3})

3.7 List and Range Operators

3.7.1 IN Operator

The IN operator determines if a given value matches any value in a list. The syntax of the operator is:

test_expression [NOT] IN (expression [,expression [,…]] )

The test_expression is any valid expression. The IN keyword is followed by a list of expressions to test for a match. The optional NOT keyword specifies that the result of the predicate be negated.

The result of an IN expression is of type Boolean. If the value of test_expression is equal to any expression from the comma-separated list, the result value is true. Otherwise, the result value is false. All expressions must be of the same type or a type compatible with test_expression.

The next example shows how the IN keyword can be applied to select certain command types of RFIDEvents:

SELECT *
FROM RFIDEvent RETAIN ALL
WHERE command IN ('OBSERVATION', 'SIGNAL')

3.7.2 BETWEEN Operator

The BETWEEN operator specifies a range to test. The syntax of the operator is:

test_expression [NOT] BETWEEN begin_expression AND end_expression

The test_expression is any valid expression and is the expression to test for the range being inclusively within the expressions defined by begin_expression and end_expression. The NOT keyword specifies that the result of the predicate be negated.

The result of a BETWEEN expression is of type Boolean. If the value of test_expression is greater then or equal to the value of begin_expression and less than or equal to the value of end_expression, the result is true.

The next example shows how the BETWEEN keyword can be used to select events with a price between 55 and 60 (inclusive).

3.8 String Operators

3.8.1 LIKE Operator

The LIKE operator provides standard SQL pattern matching. SQL pattern matching allows you to use _ to match any single character and % to match an arbitrary number of characters (including zero characters). In EPL, SQL patterns are case-sensitive by default. The syntax of LIKE is:

test_expression [NOT] LIKE pattern_expression [ESCAPE string_literal]

The test_expression is any valid expression yielding a String type or a numeric result. The optional NOT keyword specifies that the result of the predicate be negated. The LIKE keyword is followed by any valid standard SQL pattern_expression yielding a String-typed result. The optional ESCAPE keyword signals the escape character used to escape the _ and % values in the pattern.

The result of a LIKE expression is of type Boolean. If the value of test_expression matches the pattern_expression, the result value is true. Otherwise, the result value is false. An example for the LIKE keyword is shown below.

SELECT *
FROM PersonLocationEvent RETAIN ALL
WHERE name LIKE '%Jack%'

In this example the WHERE clause matches events where the suffix property is a single _ character.

SELECT *
FROM PersonLocationEvent RETAIN ALL
WHERE suffix LIKE '!_' ESCAPE '!'

3.8.2 REGEXP Operator

The REGEXP operator is a form of pattern matching based on regular expressions implemented through the Java java.util.regex package. The syntax of REGEXP is:

test_expression [NOT] REGEXP pattern_expression

The test_expression is any valid expression yielding a String type or a numeric result. The optional NOT keyword specifies that the result of the predicate be negated. The REGEXP keyword is followed by any valid regular expression pattern_expression yielding a String-typed result.

The result of a REGEXP expression is of type Boolean. If the value of test_expression matches the regular expression pattern_expression, the result value is true. Otherwise, the result value is false.

An example for the REGEXP operator is below.

SELECT *
FROM PersonLocationEvent RETAIN ALL
WHERE name REGEXP '*Jack*'

3.9 Temporal Operators

3.9.1 FOLLOWED BY Operator

The FOLLOWED BY operator specifies that first the left hand expression must turn true and only then is the right hand expression evaluated for matching events.

For example, the following pattern looks for event A and if encountered, looks for event B:

A FOLLOWED BY B

This does not mean that event A must immediately be followed by event B. Other events may occur between the event A and the event B and this expression would still evaluate to true. If this is not the desired behavior, the NOT operator can be used.

3.9.2 WITHIN Operator

The WITHIN qualifier acts like a stopwatch. If the associated pattern expression does not become true within the specified time period it is evaluated by the engine as false. The WITHIN qualifier takes a time period as a parameter as specified in Section 2.4.4, "Specifying Time Interval."

This pattern fires if an A event arrives within 5 seconds after statement creation.

A WITHIN 5 seconds

This pattern fires for all A events that arrive within 5 second intervals.

3.9.3 EVERY Operator

The EVERY operator indicates that the pattern sub-expression should restart when the sub-expression qualified by the EVERY keyword evaluates to true or false. In the absence of the EVERY operator, an implicit EVERY operator is inserted as a qualifier to the first event stream source found in the pattern not occurring within a NOT expression.

The EVERY operator works like a factory for the pattern sub-expression contained within. When the pattern sub-expression within it fires and thus quits checking for events, the EVERY causes the start of a new pattern sub-expression listening for more occurrences of the same event or set of events.

Every time a pattern sub-expression within an EVERY operator turns true the engine starts a new active sub-expression looking for more event(s) or timing conditions that match the pattern sub-expression.

This pattern fires when an A event is followed by a B event and continues attempting to match again after the B event:

EVERY (A FOLLOWED BY B)

This pattern also fires when an A event is followed by a B event, but continues attempting to match again after the A event:

EVERY A FOLLOWED BY B

The EVERY in this pattern is optional, since it would implicitly be placed here if it was absent.

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